Simviation Forum - AP/ILS questions

Nov 20^th, 2010 at 2:30am

jgf Offline
Colonel
village idiot
Columbus OH

Posts: 91

This is probably ridiculously simple but nothing I've read has given me the answer. When I enable the Approach function on the AP, do I disable the Altitude and Heading hold functions? or have all three enabled? (trial and error hasn't provided a definitive answer)

Also, my normal procedure is to come in at 2000-2200ft AGL and engage Approach when I intersect the ILS; at some airports the plane will descend to 1500-1800ft AGL then overfly the airport at that altitude; I disengage the AP, go around and try again - same results. Go around once more and land manually. (I usually let the AP fly approach til around 1000ft AGL, perhaps 500ft for small aircraft, then disengage.) What would be causing this odd behaviour?

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Reply #1 - Nov 20^th, 2010 at 7:17am

Pablo Offline
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Eat my Shorts!

Posts: 128

I always find its best to contact ATIS* when approaching the Airfield, to obtain which runway is in use, and which end of the runway I must use, (take-off and landing, depending upon the wind direction, etc), and any other important information.

It is very easy to dial in the ILS frequency and find oneself descending to the wrong end of the runway, (the far-end, back-course)... Shocked

...!

* http://en.wikipedia.org/wiki/Automatic_Terminal_Information_Service

Beauty in the "B"

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Reply #2 - Nov 20^th, 2010 at 7:28am

Crash Ex Member

Keep the heading and altitude buttons enabled. It should turn off automatically when the ILS kicks in and take your plane right down to the runway.

Carlo Wink

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Reply #3 - Nov 20^th, 2010 at 8:36am

Nav Offline
Colonel

Posts: 717

Hi! again, jgf.

You MUST contact ATC once you are within 30 miles, to get clearance and also to be advised as to which runway to use. If it's a small airport with no ATC, ATIS should give you the wind direction and 'runway in use,' then check the map for the precise runway direction etc.

Further, as Crash says, leave Altitude Hold and Heading Hold engaged and wait for the autopilot to turn them off at the right points.

More advice here:-

http://205.252.250.26/cgi-bin/yabb2/YaBB.pl?board=COF;action=display;num=1111322...

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Reply #4 - Nov 20^th, 2010 at 4:01pm

microlight Offline
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Southern UK

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One important thing to remember is that when you've captured the localizer, you must then intersect the glideslope from beneath, or else the default FS autopilot won't capture the GS, and you will stay at your set altitude.

Wink

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Reply #5 - Nov 21^st, 2010 at 2:01am

jgf Offline
Colonel
village idiot
Columbus OH

Posts: 91

microlight wrote on Nov 20^th, 2010 at 4:01pm:

One important thing to remember is that when you've captured the localizer, you must then intersect the glideslope from beneath, or else the default FS autopilot won't capture the GS, and you will stay at your set altitude.

Wink

I was advised that 2000ft was a reasonable approach altitude for ILS, so have used that since. When the gauge indicates I've intersected, I hit the approach button on the AP. I don't recall ever seeing the AP disengage the heading or altitude functions (the indicators remain lit); thought perhaps I'm taking control before the point where this would happen, but have let the AP bring the Baron all the way to touchdown with all three indicators lit.

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Reply #6 - Nov 21^st, 2010 at 2:39am

jgf Offline
Colonel
village idiot
Columbus OH

Posts: 91

Nav wrote on Nov 20^th, 2010 at 8:36am:

...
You MUST contact ATC once you are within 30 miles, to get clearance and also to be advised as to which runway to use. If it's a small airport with no ATC, ATIS should give you the wind direction and 'runway in use,' then check the map for the precise runway direction etc.
...

Usually contact my destination as soon as it appears on the 'nearest airport' list, since ATC has the irritating habit of, no matter from which direction I'm approaching, sending me to the most difficult to reach runway from my current course (they also take great delight in directing me to the one runway at the airport with no ILS).

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Reply #7 - Nov 21^st, 2010 at 6:03am

elite marksman Offline
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jgf wrote on Nov 21^st, 2010 at 2:39am:

Usually contact my destination as soon as it appears on the 'nearest airport' list, since ATC has the irritating habit of, no matter from which direction I'm approaching, sending me to the most difficult to reach runway from my current course (they also take great delight in directing me to the one runway at the airport with no ILS).

This is where the "request different runway" feature is nice... Like today when ATC decided to send me to a 5000' rwy with no ILS in <5nm visibility when there was a parallel 12000' rwy with ILS... Huh

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Reply #8 - Nov 21^st, 2010 at 7:59am

dave3cu Offline
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Quote:

..When the gauge indicates I've intersected, I hit the approach button on the AP....

The [APP]roach hold should be engaged once you are established on the HDG and ALT to intersect with the ILS, and well before intercepting the ILS glide path/slope.

APP will then automatically disengage the HDG and ALT holds as it locks on to path and then slope.

Dave

« Last Edit: Nov 21^st, 2010 at 12:38pm by dave3cu »

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Reply #9 - Nov 21^st, 2010 at 9:17am

Nav Offline
Colonel

Posts: 717

jgf wrote on Nov 21^st, 2010 at 2:01am:

I was advised that 2000ft was a reasonable approach altitude for ILS, so have used that since. When the gauge indicates I've intersected, I hit the approach button on the AP. I don't recall ever seeing the AP disengage the heading or altitude functions (the indicators remain lit); thought perhaps I'm taking control before the point where this would happen, but have let the AP bring the Baron all the way to touchdown with all three indicators lit.

As dave3cu points out, jgf, you're leaving APP far too late.

If you look at that tute of mine, all four lights (APP, HDG, IAS, and ALT) are lit in the first shot (when I'm all of 21 miles out, and still doing 220 knots). In the second shot (at about 12 miles) the A/P has turned off HDG and is lining the aeroplane up. In the fourth one (at say 6 miles) it has turned off ALT as well and is taking the aeroplane down the glideslope. In the fifth one, I've turned off the autothrottle too (although that's a personal preference, I like to do that early so I can match the manual throttle setting to the landing speed, you can leave it on much later if you like) so all the autopilot panel is showing is APP.

Hope that sorts it.

PS 2,000 or 2,500 feet is fine as a starting point. Though, of course, that's 2,000 feet AGL.

Always be sure, as part of your 'procedure,' to call up the map early on, click on the airport, and make sure that the runway at your destination isn't at THREE thousand feet!

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Reply #10 - Nov 21^st, 2010 at 8:07pm

Stewy44 Offline
Colonel
Giggety Giggety!
(Sim)Flying in Europe and Asia

Posts: 141

I use the NAV (not HDG) button on the AP to line up with the correct runway allignment when I've picked up the ILS signal. I alse have the "ALT" button on as well

Once I've picked up a glideslope, I'll watch the glidepath descend until it reaches the centre notch and then I'll hit the "APP" button to "catch" the glideslope. The "ALT" button will automatically disengage and the plane will follow the ILS down.

Works for me! Cheesy

FS9 - the only way you can fly a 747 while drinking beer

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Reply #11 - Nov 22^nd, 2010 at 2:22am

jgf Offline
Colonel
village idiot
Columbus OH

Posts: 91

Thanks for all the input. After years of just flying around (all the way back to the early days of FS98) I've been trying to learn to do things "by the book".

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Reply #12 - Nov 22^nd, 2010 at 9:49pm

Gringo6 Offline
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It's also a good idea to use the approach plates to determine what altitude and headng to use.

Frequently the approach plate will have the instrument approach to the airport begin at some fix (such as a VOR) and not just a long straight-in shot.

The aproach to Juneau AK comes to mind.

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Reply #13 - Nov 24^th, 2010 at 7:30pm

Stewy44 Offline
Colonel
Giggety Giggety!
(Sim)Flying in Europe and Asia

Posts: 141

Fly into Geneva, Switzerland - I think if you're coming from the north, the approach is huge!

FS9 - the only way you can fly a 747 while drinking beer

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